Methods for identifying modulators of eoxin formation
A method for identifying a compound for modulating the formation of 14,15-LTC4 (Eoxin C4; EoxC4), 14,15-LTD4 (Eoxin D4; EoxD4), or 14,15-LTE4 (Eoxin E4; EoxE4) in a biological system. A method for identifying a compound with an anti-inflammatory effect, the method comprising testing the compound for an effect on formation and/or activity of 14,15-LTC4 (Eoxin C4; EoxC4), 14,15-LTD4 (Eoxin D4; EoxD4), or 14,15-LTE4 (Eoxin E4; EoxE4) in a biological system. A method of making an anti-inflammatory composition or Eoxin formation-modulating composition comprising (i) identifying an anti-inflammatory compound or Eoxin formation-modulating compound by a method of the invention; (ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
The present invention relates to methods for identifying pharmaceutically useful compounds. The invention further relates to methods for identifying compounds that are useful in the treatment of inflammatory diseases and of inflammation generally. The invention also relates to a method of making an anti-inflammatory composition and methods of using pharmaceutically useful compounds.
BACKGROUND OF THE INVENTIONThere are many diseases/disorders that are inflammatory in their nature. One of the major problems associated with existing treatments of inflammatory conditions is a lack of efficacy and/or the prevalence of side effects (real or perceived).
Asthma is a chronic inflammatory disease affecting of 6% to 8% of the adult population of the industrialized world. In children, the incidence is even higher, being close to 10% in most countries. Asthma is the most common cause of hospitalization for children under the age of fifteen.
Treatment regimens for asthma are based on the severity of the condition. Mild cases are either untreated or are only treated with inhaled β-agonists. Patients with more severe asthma are typically treated with anti-inflammatory compounds on a regular basis.
There is a considerable under-treatment of asthma, which is due at least in part to perceived risks with existing maintenance therapy (mainly inhaled corticosteroids). These include risks of growth retardation in children and loss of bone mineral density, resulting in unnecessary morbidity and mortality. As an alternative to steroids, leukotriene receptor antagonists (LTRas) have been developed. These drugs may be given orally, but are considerably less efficacious than inhaled steroids and usually do not control airway inflammation satisfactorily.
This combination of factors has led to at least 50% of all asthma patients being inadequately treated.
A similar pattern of under-treatment exists in relation to allergic disorders, where drugs are available to treat a number of common conditions but are underused in view of apparent side effects. Rhinitis, conjunctivitis and dermatitis may have an allergic component, but may also arise in the absence of underlying allergy. Indeed, non-allergic conditions of this class are in many cases more difficult to treat.
Chronic obstructive pulmonary disease (COPD) is a common disease affecting 6% to 8% of the world population. The disease is potentially lethal, and the morbidity and mortality from the condition is considerable. At present, there is no known pharmacological treatment capable of changing the course of COPD.
Other inflammatory disorders which may be mentioned include:
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- (a) idiopathic pulmonary fibrosis (this is less common than COPD, but is a serious disorder with a very bad prognosis. No curative treatment exists);
- (b) inflammatory bowel disease (a group of disorders with a high morbidity rate. Today only symptomatic treatment of such disorders is available); and
- (c) rheumatoid arthritis and osteoarthritis (common disabling inflammatory disorders of the joints. There are currently no curative, and only moderately effective symptomatic, treatments available for the management of such conditions).
Inflammation is also a common cause of pain. Inflammatory pain may arise for numerous reasons, such as infection, surgery or other trauma. Moreover, several malignancies are known to have inflammatory components adding to the symptomotology of the patients.
Thus, a new and/or alternative anti-inflammatory treatment would be of benefit to all of the above-mentioned patient groups. In particular, there is a real and substantial unmet clinical need for an effective anti-inflammatory drug capable of treating inflammatory disorders, such as asthma, with no real or perceived side effects.
The mammalian lipoxygenases are a family of structurally related enzymes, which catalyse the oxygenation of arachidonic acid leading to the formation of various pro-inflammatory mediators. Three types of human lipoxygenases are known which catalyse the insertion of molecular oxygen into arachidonic acid at carbon positions 5, 12 and 151. The enzymes are hence named 5-, 12- and 15-lipoxygenase, respectively.
Arachidonic acid metabolites that are formed following the action of lipoxygenases are known to have pronounced pathophysiological activity including pro-inflammatory effects.
The key enzyme in leukotriene biosynthesis is 5-lipoxygenase which in a two step-reaction converts arachidonic acid to leukotriene (LT)A4. This metabolite can be hydrolysed enzymatically to leukotriene B4 (LTB4) or conjugated with glutathione, by leukotriene C4 (LTC4) synthase, to form LTC4, which in turn can be cleaved by sequential action of γ-glutamyl-transpeptidase and dipeptidase to yield leukotriene D4 (LTD4) and leukotriene E4 (LTE4), respectively. LTC4 and its metabolites are pro-inflammatory agents and potent bronchoconstrictors2.
Huge efforts have been devoted towards the development of drugs that inhibit the action of these metabolites as well as the biological processes that form them. Drugs that have been developed to this end include 5-lipoxygenase inhibitors and, as mentioned previously, leukotriene receptor antagonists (LTRas). Inhibitors of FLAP (Five Lipoxygenase Activating Protein) have also been investigated.
Another class of enzymes that metabolize arachidonic acid are the cyclooxygenases. Arachidonic acid metabolites that are produced by this process include prostaglandins, thromboxanes and prostacyclin, all of which possess physiological or pathophysiological activity. In particular, the prostaglandin PGE2 is a strong pro-inflammatory mediator, which also induces fever and pain. Consequently, a number of drugs have been developed to inhibit the formation of PGE2, including “NSAIDs” (non-steroidal antiinflammatory drugs) and “coxibs” (selective cyclooxygenase-2 inhibitors). These classes of compounds act predominantly by way of inhibition of one or several cyclooxygenases. In addition receptor antagonists are being investigated.
Thus, in general, agents that are capable of blocking the formation of arachidonic acid metabolites are likely to be of benefit in the treatment of inflammation.
Pro-inflammatory agents may also be useful, for example in immunosuppressed patients, for example patients undergoing chemotherapy, treatment to prevent graft rejection or patients with AIDS.
In addition to 5-lipoxygenase 12- and 15-lipoxygenase are also expressed in the human body.
12-lipoxygenase (12-LO) is expressed to high extent in human platelets but very little is known about the biological role of this enzyme1.
15-lipoxygenase (15-LO) type 1 (human 15-LO:EC 1.13.11.33) is a 75-kDa protein containing a non-heme iron. 15-LO introduces molecular oxygen at C-15 of arachidonic:acid (20:4) or at C-13 of linoleic acid (18:2) to form 15S-hydroperoxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HPETE) or 13S-hydroperoxy-9-cis-13-trans-octadecadienoic acid (13-HPODE), respectively. A small amount of 12S-hydroperoxy-5,8,14-cis-10-trans-eicosatetraenoic acid (12-HPETE) is also formed from arachidonic acid by the 15-LO enzyme. Briefly, the catalytic reaction involved hydrogen abstraction at C-3 of the cis-cis-1,4-pentadiene structure of the unsaturated fatty acid (20:4 or 18:2), leading to a carbon radical and reduction of the iron from Fe3+ to Fe2+ (see scheme 1 below).
The radical migrates to C-5 where it reacts with molecular oxygen to form a peroxy radical. Oxidation of the iron to Fe3+ by the peroxy radical yields a peroxy-anion that is protonated to give the final lipidhydroperoxide.
The rabbit enzyme 15-LO has been cloned and crystallised and the substrate-binding site was found to be a deep hydrophobic pocket22, which is defined at its base by the side chains of Phe353, Met419, Ile418 and Ile593. The fatty acid substrate is tethered and positioned by Arg403 (on the surface of the enzyme). Mutagenic studies have demonstrated that variation of the size of the hydrophobic pocket affects the positional specificity of the enzyme. Thus, enlargement of the pocket of 15-LO increased the amount of 12-lipoxygenation products (12-HPETE). The iron in 15-LO is liganded to histidines and to the carboxy group of a C-terminal isoleucine.
In addition to undergoing reduction to 15(S)-HETE, 15 (S)-HPETE may also undergo dehydration to form 14,15-oxido-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTA4). This allylic epoxide can be hydrolysed to the dihydroxy acids 8 (R,S), 15(S)-LTB4 or 14 (R,S), 15(S)-LTB411-12. In addition, with 15-HPETE as a substrate, 15-LO can also catalyse the formation of the double dioxygenation products 5(S), 15 (S)-DHETE, 8 (S,R), 15 (S)-DHETE and 14 (R,S), 15 (S)-DHETE.
15(S)-lipoxygenase (15-LO) does not only metabolise free fatty acids but can also attack polyenoic fatty acids located in the membrane. The enzyme has been predicted to play an important role in reticulocyte maturation through breakdown of mitochondria membranes3. However, the enzyme may play a more general role in the differentiation of cells, such as maturation of keratinocytes and the eye lens4. 15-LO is predominantly expressed in reticulocytes, eosinophils, skin, monocytes/macrophages and airway epithelium5. Interleukin-4 (IL-4) and interleukin-13 (IL-13) induce the expression of 15-LO in cultivated monocytes and epithelial cells6, but also damage to certain cells has been reported to increase the activity of 15-LO (Green F A. Transformation of 5-HETE by activated keratinocyte 15-lipoxygenase and the activation mechanism. Lipids 25, 618-623 (1990)).
In contrast to 5-lipoxygenase and 12-lipoxygenase, 15-LO appears to be expressed only in rabbit and human cells1. The murine ortholog of the human 15-LO appears to be leukocyte-type 12-LO1. However, the regulation of the two enzymes activities seems to be quite different7.
15-LO was discovered more than two decades ago and the first 15-LO to be purified to homogeneity was derived from rabbit reticulocytes8. The human form of the enzyme has been cloned from reticulocytes and epithelial cells, and immunological studies indicate that the enzyme is identical in reticulocytes, eosinophils and airway epithelium9. A second form of 15-LO (type 2) has been cloned from a cDNA library from human hair roots and subsequently expression of the enzyme and amino acid analysis demonstrated that this 15-LO type 2 enzyme was approximately 40% identical to the earlier described 15-LO type 110.
15-LO is thought to be involved in the formation of lipoxins, which mainly seem to have anti-inflammatory effects13, but a 15-LO derived product, 5-oxo-15-hydroxy-6,8,1,13-eicosatetraenoic acid, has been reported to be a potent chemotactic agent for human eosinophils14. The physiological and pathophysiological roles of the 15-LO pathway in humans have not been fully characterised.
Based on arachidonic acid metabolites which are known to occur in biological systems for example leukotrienes, a number of different analogues have been synthesised. Synthetic analogues of LTC4, such as 14,15-LTC4 did not induce bronchoconstriction. Drazen, J. M., Lewis, R. A., Austin, K. F., Toda, M., Brion, F., Marfat, A. and Corey, E. J.: Contractile activities of structural analogs of leukotrienes C and D: necessity of a hydrophobic region. Proc. Natl. Acad. Sci. 78, 3195-3198 (1981).
SUMMARY OF THE INVENTIONWe have identified the generation in biological systems of arachidonic acid metabolites with pro-inflammatory effects. The metabolites can be formed via the action of 15-lipoxygenase and via the action of soluble glutathione S transferases and/or leukotriene C4 synthase. The metabolites are termed Eoxin C4, Eoxin D4 and Eoxin E4. We provide screens for identifying anti-inflammatory compounds and compounds that inhibit Eoxin C4, D4 and E4 formation.
We show that the Hodgkin cell line L123615 possesses 15-lipoxygenase (15-LO) type 1 activity and converts arachidonic acid to Eoxins via the 15-LO pathway. Having revealed the presence and formation of Eoxin C4, D4 and E4 in L1236, we also show that these Eoxins are formed in other human cells and tissues, in particular eosinophils, but also by nasal polyp tissue and dendritic cells (Example 2). We also show that a broad variety of cell types express 15-LO. Interestingly, cells in patients suffering from an inflammatory disease or a disease involving inflammatory processes, such as Reed-Sternberg cells in lymph-nodes from patients with Hodgkin's lymphoma, epitheloid cells in lung biopsies from sarcoidosis patients, synoviocytes from rheumatoid arthritis and neurones from patients suffering from Alzheimer's Disease (Example 3) display an increased expression of 15-LO, compared to control cells.
In addition to demonstrating the biosynthesis of these new metabolites, and identifying enzymes involved, biological effects of Eoxins are also described. For example, in Example 6a, it is indicated that Eoxins C4, D4 and E4 are about 100 times more potent that histamine in causing permeabilisation of endothelial cells, (an in vitro model of inflammation), showing comparable potency to the sister metabolite, LTC4, formed through the 5-LO pathway. For example, Eoxins C4, D4 and E4 induce significant plasma leakage at 10−7 and 10−8 M in a model system with confluent bovine or human endothelial cells. In another model of inflammation, EoxC4 and EoxD4 induced mainly oxygen free radical production by GM-CSF primed neutrophils, while EoxE4 induced mainly oxygen free radical production by IL-5 primed eosinophils. We also demonstrate compounds that block the formation of Eoxins C4, D4 and E4.
We identify three 15-lipoxygenase derived metabolites from arachidonic acid, termed Eoxins: 14,15-LTC4, 14,15-LTD4, and 14,15-LTE4, named Eoxin C4 (EoxC4), Eoxin D4 (EoxD4) and Eoxin E4 (EoxE4), respectively.
Formation of the 15-LO derived cysteinyl-containing products Eoxin C4, D4 and E4 from arachidonic acid have never before been described in eukaryotic or prokaryotic cells.
The metabolites were isolated using RP-HPLC and the structures of the metabolites were determined by negative-ion electrospray tandem mass spectrometry. The Eoxins have a conjugated triene structure demonstrating an UV absorbance maximum at 282 nm (Example 1). We consider that these metabolites are formed by 15-LO catalysed conversion of arachidonic acid to 14,15-oxido-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTA4; Eoxin A4), which is conjugated with glutathione to form 14 (R)-glutathionyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTC4; Eoxin C4), which is subsequently metabolised to 14 (R)-cysteinyl-glycyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTD4; Eoxin D4) and 14 (R)-cysteinyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTE4; Eoxin E4).
The enzymes involved in the formation of 14,15-LTC4 (Eoxin C4) from 14,15-LTA4 (Eoxin A4) are considered to be LTC4-synthase and/or the soluble glutathione S-transferases (GST), in particular GSTM1, and GSTP1, as discussed in Example 4.
The suggested pathway is shown below:
A first aspect of the invention provides a method for identifying a compound for modulating the formation of Eoxin C4, Eoxin D4 or Eoxin E4 in a biological system, the method comprising testing the compound for an effect on 15-LO activity or GSTM1-1, GSTP1-1 and/or leukotriene C4 synthase activity.
A second aspect of the invention provides a method for identifying a compound with an inflammation-modulating effect or bone loss-modulating (typically bone-loss-reducing) effect, the method comprising testing the compound for an effect on formation and/or activity of Eoxin C4, Eoxin D4 or Eoxin E4 in a biological system.
By “modulating the formation” is included inhibiting or promoting the formation and/or activity of Eoxin C4, D4 or E4. Typically, the method may be used for identifying a compound for inhibiting the formation and/or activity of EoxC4, EoxD4 or EoxE4. Such a compound is considered to be an anti-inflammatory compound. Such a compound is also considered to be a bone-loss-reducing compound. The compound may typically inhibit the formation and/or activity of EoxC4, EoxD4 and EoxE4.
The method may alternatively be used for identifying a compound for promoting the formation and/or activity of EoxC4, EoxD4 or EoxE4. Such a compound is considered to be pro-inflammatory. Such a compound may typically promote the formation of EoxC4, EoxD4 and EoxE4.
The method of the first aspect of the invention may further comprise the step of testing the compound for an effect on formation or activity of EoxC4, EoxD4 or EoxE4 in a biological system.
The biological system typically comprises 15-LO, glutathione S transferase (typically a soluble glutathione S transferase, for example GSTM1-1 or GSTP1-1) and/or leukotriene C4 synthase activity.
The compound may be tested in a system comprising a cell fraction or isolated enzyme or enzymes, as discussed further below. Alternatively, the method of the first or second aspect of the invention may be performed by testing the effect of the test compound on a whole cell. For example, the method may be performed using ex vivo human cells or cell lines. For example, human eosinophils or mast cells (for example cord blood derived mast cells, for example as described in Example 8) or L1236 cell line cells may be used, but human nasal polyp tissue and/or dendritic cells or any other cell or cell-line expressing the necessary enzymes (either endogenous or recombinant); for example 15-LO and/or GST could also be used. However, it is not necessary to have co-location of the enzymes involved in this type of metabolic pathway. A well-known phenomenon in the formation of various arachidonic acid metabolites is transcellular biosynthesis, i.e. the first enzymatic step is catalysed in one cell type and the intermediate is exported to another cell type in which the second enzymatic step is performed. For example, biosynthesis of Eoxin A4 may occur in one cell type, whilst conversion of Eoxin A4 to Eoxin C4 (and optionally also conversion of Eoxin C4 to Eoxin D4 and Eoxin E4) may occur in a second cell type. Thus, the test could also be carried out in co-incubations of two cell types with complementing enzymatic capacities for the biosynthesis of Eoxins.
As will be apparent to the skilled person, it may be necessary to stimulate the cell before or as part of the assay procedure; or provide arachidonic acid in the assay, for example as described in the Examples. Eosinophils can be stimulated to produce EoxC4 by LTC4, Prostaglandin D2 or IL-5, as discussed in Example 8. It may be desirable to prime mast cells, for example using IL-4, in order to induce the expression of 15-LO-1; and then provide arachidonic acid in the assay, as discussed in Example 8. Other cells may not require stimulation in order to be able to release Eoxins. For example, human nasal polyp cells are considered to be able spontaneously to release Eoxins, as discussed in Example 8.
As will be apparent to the skilled person, if effects on the formation of Eoxin C4 are being tested for, then it may not be necessary to have present enzymes involved in the biosynthesis of metabolites of Eoxin C4, (for example γ-glutamyl-transpeptidase or dipeptidase). Similarly, if effects on 15-LO activity are being tested for, then it may not be necessary to have present enzymes involved in the biosynthesis of metabolites of the 15-LO product (Eoxin A4), for example LTC4 synthase or a soluble glutathione S transferase, for example GSTM1-1 or GSTP1-1. As will be apparent to those skilled in the art, it may be desirable to test compounds both in systems in which one or a limited number of enzymes are present; and in systems in which more enzymes (for example all of the enzymes involved in Eoxin synthesis from arachidonic acid, for example 15-LO; LTC4 synthase or a soluble GST such as GSTM1-1 or GSTP1-1; γ-glutamyl-transpeptidase and dipeptidase) are present. Tests in single or limited enzyme systems may be useful in establishing structure-function relationships, as well known to those skilled in the art; whilst tests in more complex systems may be useful in establishing whether a compound is likely to be useful in vivo.
Suitable ways to test if a compound is capable of inhibiting the formation of Eoxin C4, Eoxin D4 or Eoxin E4, as described above, are illustrated in Example 7. However, other cell lines may alternatively be used, if they have the enzymatic machinery to generate the Eoxin, the modification to the procedure depending on the cell type being evident to the person skilled in the art.
The eoxins can be detected and quantified by e.g. HPLC, gas chromatography, mass spectrometry, UV spectroscopy and different immunological methods such as EIA and RIA.
Presently, two forms of the 15-LO enzyme have been cloned, as noted above. Type 2 15-LO is approximately 40% identical to the Type 1 15-LO. In contrast to 15-LO type 1, linoleic acid is a poor substrate for 15-LO type 2. With present knowledge, the preferred enzyme for inhibition is thus 15-LO type 1, but 15-LO type 2 cannot be excluded as an enzyme in the metabolic pathway leading to the formation of Eoxins C4, D4 and E4.
The catalytic activity of 15-LO can e.g. be measured as described9. The enzyme can be assayed by assessing conversion of arachidonic acid (substrate) into 15-(s)-HETE or linoleic acid (substrate) to 13-hydroxyoctadecadienoic acid (13-HODE), in the presence or absence of the test compound in question. A decrease in the formation of 15-(S)-HETE or 13-HODE when the compound is present illustrates a decrease in enzymatic activity. Such a compound will block the first enzymatic step in the formation of Eoxins C4, D4 and E4. Such a compound is considered to have anti-inflammatory actions in vivo.
In one aspect of the first aspect of the invention, an assay for testing the catalytic activity of human 15-LO is envisioned as described in Example 5. The assay illustrated herein takes advantage of the ability of lipidhydroperoxides to oxidize diphenyl-1-pyrenylphosphone (DPPP) to a phosphine oxide. Diphenyl-1-pyrenylphosphine is a non-fluorescent compound until oxidized. Oxidation of DPPP yields a fluorescent compound, which is not sensitive to temperature and is stable for at least 60 minutes.
In another aspect of the first aspect of the invention, the assay is performed in a cell lysate to determine the conversion of arachidonic acid to 15-(S)-HETE or linoleic acid (substrate) to 13-hydroxyoctadecadienoic acid (13-HODE), in the presence or absence of the test compound in question.
Another of the key enzymes in the formation of said novel 15-lipoxygenase catalysed arachidonic acid metabolite is soluble GST. As illustrated in Example 4, GSTM1-1, GSTP1-1 and/or LTC4 synthase can participate in the formation of Eoxins C4, D4 and E4. Thus, in an embodiment of the first aspect of the invention, the effect of a test compound on the catalytic activity of GSTM1-1, GSTP1-1 and/or LTC4 synthase is assessed. An assay for the catalytic activity of GSTM1-1 or GSTP1-1 can be performed essentially as described in Example 4.
In an embodiment of the second aspect of the invention, the test compound is assessed for its ability to modulate Eoxin C4, D4 or E4 induced permeabilisation of endothelial cells in an in vitro model of inflammation, such as the one described in Example 6a. Such a test may also be performed in conjunction with a method of the first aspect of the invention.
The compound may be tested in an animal or ex vivo model of inflammation in which 15-LO is present, for example in a rabbit model of inflammation, or in a transgenic animal (for example a mouse or rat) which expresses 15-LO. The compound may be tested in a human ex vivo model of inflammation, for example on human peripheral blood or human umbilical cord blood, or on cells isolated from human peripheral blood or human umbilical cord blood, for example on leukocytes, for example neutrophils, eosinophils, dendritic cells or mast cells. Examples of such tests are described in the Examples, for example Example 6b. The compound may also be tested for ability to differentiate stem cells or other bone-forming cell precursors into bone cells, for example as described in US 2003/0175680.
The compounds to be tested may be selected on the basis of structure-based screening methods, for example in which compound structures are compared with or designed or modified on the basis of the substrate binding site of 15-LO, as discussed above. A starting compound may initially be selected by screening for an effect on 15-LO enzyme activity (for example using an assay as described in Example 5); then compared with the structure; used as the basis for designing further compounds which may then be tested by further modelling and/or synthesis and assessment, for example for an effect on Eoxin C4, D4 or E4 formation.
Assessment of effects on 15-LO activity using DPPP (for example as described in Example 5) means that a spectrophotometric assay can be used, is straightforward to perform and can be used in, for example, a microtitre plate format which is very suitable for high throughput testing. Assessment using arachidonic acid or 15-HPETE or other arachidonic acid metabolite as the substrate, may be useful in confirming the ability of a compound to modulate 15-LO activity in vivo.
Compounds may also be subjected to other tests, for example toxicology or metabolism tests, as is well known to those skilled in the art.
It will be appreciated that the invention provides screening assays for use in trying to identify drugs which may be useful in modulating, for example either enhancing or inhibiting, the formation or activity of one or more of Eox C4, Eox D4 and Eox E4. Compounds identified in the methods may themselves be useful as a drug or they may represent lead compounds for the design and synthesis of more efficacious compounds.
The compound may be a drug-like compound or lead compound for the development of a drug-like compound for each of the above methods of identifying a compound. It will be appreciated that the said methods may be useful as screening assays in the development of pharmaceutical compounds or drugs, as well known to those skilled in the art.
The term “drug-like compound” is well known to those skilled in the art, and may include the meaning of a compound that has characteristics that may make it suitable for use in medicine, for example as the active ingredient in a medicament. Thus, for example, a drug-like compound may be a molecule that may be synthesised by the techniques of organic chemistry, less preferably by techniques of molecular biology or biochemistry, and is preferably a small molecule, which may be of less than 5000 daltons. A drug-like compound may additionally exhibit features of selective interaction with a particular protein or proteins and be bioavailable and/or able to penetrate cellular membranes, but it will be appreciated that these features are not essential.
The term “lead compound” is similarly well known to those skilled in the art, and may include the meaning that the compound, whilst not itself suitable for use as a drug (for example because it is only weakly potent against its intended target, non-selective in its action, unstable, difficult to synthesise or has poor bioavailability) may provide a starting-point for the design of other compounds that may have more desirable characteristics.
It is appreciated that screening assays which are capable of high throughput operation are particularly preferred. Enzyme assays using DPPP may be used, as discussed above.
It will be understood that it will be desirable to identify compounds that may modulate, as appropriate, inflammation or the formation or activity of Eoxins C4, D4 or E4 in vivo. Thus it will be understood that reagents and conditions used in the methods of the invention may be chosen such that the interactions between, for example, the 15-LO and the substrate, are similar to those between the human 15-LO and a naturally occurring substrate (for example arachidonic acid). As well known to those skilled in the art, different assay systems may be used to assess a compound, in some of which the convenience of the assay or the specificity for an effect on a particular enzyme involved in Eoxin formation may be optimised (for example using a single enzyme system), whilst in others the in vivo relevance may be optimised, for example by assessing the effect of the compound in a whole cell.
The screening assays of the invention are useful in the search for compounds which may be useful in the treatment of inflammatory disease or in a disease involving inflammatory processes. A compound selected on the basis of in vitro and/or in vivo screens may be further tested for an anti-inflammatory effect in an inflammatory disease or in a disease involving inflammatory processes. Similarly, the screening assays of the invention are useful in the search for compounds which may be useful in treating or preventing bone loss/enhancing bone formation. A compound selected on the basis of in vitro and/or in vivo screens may be further tested for a bone-loss-reducing/bone-formation-enhancing effect in a patient with or at risk of bone loss or in a disease involving inflammatory processes.
The term “inflammation” will be understood by those skilled in the art to include any condition characterised by a localised or a systemic protective response, which may be elicited by physical trauma, infection, chronic diseases, such as those mentioned hereinbefore, and/or chemical and/or physiological reactions to external stimuli (e.g. as part of an allergic response). Any such response, which may serve to destroy, dilute or sequester both the injurious agent and the injured tissue, may be manifest by, for example, heat, swelling, pain, redness, dilation of blood vessels and/or increased blood flow, invasion of the affected area by white blood cells, loss of function and/or any other symptoms known to be associated with inflammatory conditions.
The term “inflammation” will thus also be understood to include any inflammatory disease, disorder or condition per se, any condition that has an inflammatory component associated with it, and/or any condition characterised by inflammation as a symptom, including inter alia acute, chronic, ulcerative, specific, allergic and necrotic inflammation, and other forms of inflammation known to those skilled in the art. The term thus also includes, for the purposes of this invention, inflammatory pain and/or fever.
It is considered that a compound that decreases formation or activity of Eoxins C4, D4 or E4 will be useful in treating an inflammatory disease or a disease involving inflammatory processes. Accordingly, the screening methods of the invention are useful in identifying compounds which may be useful in the treatment of asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, allergic disorders, rhinitis, inflammatory bowel disease, ulcers, inflammatory pain, fever, atherosclerosis, coronary artery disease, vasculitis, pancreatitis, arthritis, osteoarthritis, rheumatoid arthritis, conjunctivitis, iritis, scleritis, uveitis, wound healing, dermatitis, eczema, psoriasis, stroke, diabetes, autoimmune diseases, Alzheimer's disease, multiple sclerosis, sarcoidosis, atherosclerosis, hypertension (see, for example Anning P B et al (March 2005) Elevated endothelial nitric oxide bioactivity and resistance to angiotensin-dependent hypertension in 12/15-lipoxygenase knockout mice. Am J. Pathol. 166(3):653-62), Hodgkin's lymphoma and other malignancies, or any other disease with an inflammatory component.
The screening methods of the invention are also considered to be useful in identifying compounds which may be useful in the treatment or prevention of bone loss, for example associated with osteoporosis, osteoarthritis, Paget's disease or periodontal diseases, as discussed in US 2003/0175680. The screening methods of the invention may thus also be useful in identifying compounds which may be useful in increasing bone mineral density, as well as the reduction in incidence and/or healing of fractures, in subjects.
The compounds may be useful both in the therapeutic and/or prophylactic treatment of the above-mentioned conditions.
It is considered that a compound that increases formation or activity of Eoxins C4, D4 or E4 will be useful in treating a patient in which promotion of an inflammatory response may be beneficial, for example in an immunosuppressed patient, for example a patient undergoing chemotherapy or treatment to reduce rejection of a transplant. Eox C4, Eox D4 or Eox E4, for example, are considered to be useful in treating such a patient in which promotion of an inflammatory response may be beneficial.
Accordingly, a further aspect of the invention provides a method for treating a patient in need of promotion of an inflammatory response, the method comprising administering to the patient a therapeutically effective amount of Eox C4, Eox D4 or Eox E4. A further aspect of the invention provides the use of Eox C4, Eox D4 or Eox E4 in the manufacture of a medicament for treating a patient in need of promotion of an inflammatory response.
As a result of performing a screening method of the invention a compound is identified, which may typically be a peptide or a small molecule, for example as shown by Example 7. The compound can be formulated for pharmaceutical use, for example for use in in vivo trials in patients, for example animals (typically mammals, for example experimental mammals such as mice, rats, rabbits, dogs or monkeys, preferably rabbits or other animals (eg transgenic animals) which express 15-LO) or humans.
A third aspect of the invention provides a method of making an anti-inflammatory composition or bone-loss-reducing composition comprising
(i) identifying respectively an anti-inflammatory or bone-loss-reducing compound by a method of the second aspect of the invention;
(ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
A fourth aspect of the invention provides a method of making an Eoxin formation-modulating composition comprising
(i) identifying an Eoxin formation-modulating compound by a method of the first aspect of the invention;
(ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
The composition is typically intended to supply an effective amount of the compound to a patient. The term “effective amount” refers to an amount of a compound, which confers a therapeutic effect on the treated patient. The effect may be objective (i.e. measurable by some test or marker) or subjective (i.e. the subject gives an indication of or feels an effect).
The composition may be intended for or suitable for administering orally, intravenously, subcutaneously, buccally, rectally, dermally, nasally, tracheally, bronchially, sublingually, by any other parenteral route or via inhalation, in a pharmaceutically acceptable dosage form. The composition may be, for example, a tablet, capsule or elixir for oral administration, suppository for rectal administration, sterile solution or suspension for parenteral or intramuscular administration, and the like. It may be a spray for inhalation or a liquid for injection. Such compositions may be prepared in accordance with standard and/or accepted pharmaceutical practice.
The composition may also contain another therapeutic agent that is useful in the treatment of inflammation as defined herein (e.g. selected from NSAIDs, coxibs, corticosteroids, analgesics, inhibitors of 5-lipoxygenase, inhibitors of FLAP (5-lipoxygenase activating protein), and leukotriene receptor antagonists (LTRas), and/or other therapeutic agents that are useful in the treatment of inflammation).
Alternatively, the composition may also contain another therapeutic agent that is useful in reducing bone loss or increasing bone formation, for example a biosphosphonate, estrogen, selective estrogen receptor modulator (SERM), calcinonin or an anabolic agent. Examples of such therapeutic agents are discussed in, for example, US 2003/0175680, for example in paragraph [0065].
Such combination products provide for the administration of the identified compound in conjunction with the other therapeutic agent, and may thus be presented either as separate formulations, wherein at least one of those formulations comprises the identified, and at least one comprises the other therapeutic agent, or may be presented (i.e. formulated) as a combined preparation (i.e. presented as a single formulation including the identified compound and the other therapeutic agent).
Compounds may be administered at varying doses. Oral, pulmonary and topical dosages may range from between about 0.01 mg/kg of body weight per day (mg/kg/day) to about 100 mg/kg/day, preferably about 0.01 to about 10 mg/kg/day, and more preferably about 0.1 to about 5.0 mg/kg/day. For e.g. oral administration, the compositions typically contain between about 0.01 mg to about 500 mg, and preferably between about 1 mg to about 100 mg, of the active ingredient. Intravenously, the most preferred doses will range from about 0.001 to about 10 mg/kg/hour during constant rate infusion. Advantageously, compounds may be administered in a single daily dose, or the total daily dosage may be administered in divided doses of two, three or four times daily.
In any event, the physician, or the skilled person, will be able to determine the actual dosage which will be most suitable for an individual patient, which is likely to vary with the route of administration, the type and severity of the condition that is to be treated, as well as the species, age, weight, sex, renal function, hepatic function and response of the particular patient to be treated. The above-mentioned dosages are exemplary of the average case; there can, of course, be individual instances where higher or lower dosage ranges are merited, and such are within the scope of this invention. Example 7, for example, shows a method by which compounds that are capable of inhibiting the formation of Eoxins are identified.
The invention will now be described further by reference to the following, non-limiting, Figures and Examples.
Insert: UV-spectrum of the material eluting under peak V.
a) Time course of the formation of 14,15-LTC4 and 14,15-LTD4 after incubation with 40 μM arachidonic acid.
b) Dose-response curve of the formation of 14,15-LTC4 and 14,15-LTD4 after 5 min incubation with various concentrations of arachidonic acid as indicated.
a) HPLC chromatogram of the products formed. Co-elution with synthetic standards for Eoxin C4, LTC4, 8,15-DHETEs (see
b) UV spectrum of the material under the peak co-eluting with synthetic Eoxin C4.
A) supernatant and B) membrane fraction.
a. Purified blood neutrophils stimulated (filled symbols) or GM-CSF treated and subsequently stimulated (open symbols) to produce oxygen free radicals. “BLX-26” is used to indicate BLX-926.
b: EoxD4 (BLX-926) induced oxygen free radical by GM-CSF-primed neutrophils. Results show total radical production and are presented as % of Control (primed cells) and as mean+/−se, n=13
c: Scatter plot showing EoxD4 (BLX-926) induced oxygen free radical by GM-CSF-primed neutrophils. Results show total radical production measured as count per minute (CPM×106), n=13. The line shows the reference line (k=1), indicating that all observations above the line are responders to the stimuli.
a: Purified blood eosinophils stimulated (filled symbols) or IL-5 treated and subsequently stimulated (open symbols) to produce oxygen free radicals. “BLX-27” is used to indicate BLX-927.
b: Stimulation and EoxE4 (BLX-927) induced oxygen free radical by IL-5 primed eosinophils. Results show total radical production and are presented as % of Control (primed cells) and as mean+/−se, n=6
c: Scatter plot showing EoxE4 (BLX-927) induced oxygen free radical by IL-5 primed eosinophils. Results show total radical production measured as count per minute (CPM×106), n=6. The line shows the reference line (k=1), indicating that all observations above the line are responders to the stimuli.
Synthetic 14,15-oxido-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTA4), 14 (R)-glutathionyl-15 (S)-hydroxy-5,8,10,10 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTC4), 14 (R)-cysteinyl-glycyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTD4), 14 (R)-cysteinyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTE4), 8 (R), 15 (S)-dihydroxy-5,9,11,13 (Z,E,E,E)-eicosatetraenoic acid (8 (R), 15 (S)-LTB4), 8 (S), 15 (S)-dihydroxy-5,9,11,13 (Z,E,Z,E)-eicosatetraenoic acid (8 (S), 15(S)-DHETE), 8 (S), 15 (S)-dihydroxy-5,9,11,13 (Z,E,E,E)-eicosatetraenoic acid (8 (S), 15 (S)-LTB4), 8 (R), 15 (S)-dihydroxy-5,9,11,13 (Z,E,Z,E)-eicosatetraenoic acid (8 (R), 15 (S)-DHETE), 14 (R), 15 (S)-dihydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14 (R), 15 (S)-DHETE or 14 (R), 15 (S)-LTB4), 15 (S)-hydroxy-5,8,11,13 (Z,Z,Z,E)-eicosatetraenoic acid (15-HETE), 12 (S)-hydroxy-5,8,10,14 eicosatetraenoic acid (Z,Z,E,Z) (12 (S)-HETE) and 13 (S)-hydroxyoctadeca-9,11 (Z,E)-dienoic acid (13 (S)-HODE) were from Biomole Inc. (Plymouth Meeting, USA). Cell culture medium RPMI 1640, foetal calf serum, penicillin, streptomycin and glutamine were obtained from Gibco, BRL. HPLC solvents were obtained from Rathburn Chemicals (Walkerburn, United Kingdom).
L1236 Cell LineThe cell line L1236 was originally generated from the peripheral blood of a patient suffering from Hodgkin's lymphoma (HL) of mixed cellularity subtype15. The cells were grown in suspension at 37° C. in an atmosphere of 5% CO2. Culture medium was RPMI 1640 containing 100 U/ml penicillin and 100 μg/ml streptomycin supplemented with 10% foetal calf serum and 2 mM glutamine.
Experimental Conditions and HPLC AnalysisThe cell suspensions were centrifuged at 200×g for 5 min and the pellet was suspended in PBS. After washing twice in PBS, the cells were solved in PBS at a concentration of 10-20×106 cells/ml. The sample was prewarmed for 2 minutes at 37° C. prior to the addition of arachidonic acid, 14,15-LTA4 or other indicated metabolite and subsequently incubated for the period indicated. The incubations were terminated by addition of 3 vol. ice-cold methanol. Precipitated proteins and cell fragments were removed by centrifugation and excess water and ethanol were evaporated under reduced pressure. The residues were solved in methanol and transferred to a test tube and evaporated to dryness under a stream of nitrogen. Subsequently, the residues were reconstituted in the chromatographic solvent described below. The samples were applied to an octadecyl reverse-phase column (Chromabond, C18, 100 mm, Macherey-Nagal, Duren, Germany), eluted at a flow rate of 0.4 ml/min. The mobile phase was acetronitrile/methanol/water/acetic acid (28:18:72:0.8, by vol., pH adjusted to 5.6 with 30% NaOH) or methanol/water/acetic acid (72.5:27.5:0.01, by vol) for analysis of cysteinyl-containing arachidonic acid metabolites and dihydroxy acids or monohydroxy acids, respectively. Eluted metabolites were detected and quantified utilising a programmable Waters 991 diode array spectrophotometer.
Negative-Ion Electrospray Tandem Mass SpectrometrySpectra were recorded on a hybrid magnetic sector/time of flight tandem instrument at laboratory frame collision energy of 400 eV with Xe as the collision gas as described16.
ResultsIncubation of L1236 cells with arachidonic acid for 10 min led to the formation of a major product, which co-chromatographed with synthetic 15 (S)-HETE (
In addition to the peaks absorbing UV at 236 nm a number of peaks with UV absorbance maximum around 270 nm and retention times between 5-7 min were observed in the chromatogram. An acetonitrile based mobile phase was used to get separation of these products.
In order to elucidate the mechanism of formation and double bond structure of 14, 15-LTC4 and 14, 15-LTD4, the cells were incubated with 2 μM synthetic 14, 15-oxido-5,8,10,12 (Z,Z,EE)-eicosatetraenoic acid (14, 15-LTA4) for 30 min.
An overview of the 15-LO pathway and the suggested pathway for the biosynthesis of the 14, 15-LTC4, 14, 15-LTD4 and 14, 15-LTE4 is shown in
The time-courses of the formation of 14, 15-LTC4 and 14, 15-LTD4 after incubation with arachidonic acid (40 μM) are shown in
14, 15-LTC4; 14, 15-LTD4 and 14, 15-LTE4 have been named, Eoxin C4, Eoxin D4 and Eoxin E4, respectively.
EXAMPLE 2 Demonstration of the Biosynthesis of Eoxin C4 (14, 15-LTC4) in Other Cells and Tissues Material and Methods Isolation of Human EosinophilsVenous blood (100 ml) was drawn from healthy volunteers or from patients with eosinophilia, including hypereosinophilic syndrome (HES), chronic lymphocytic leukaemia (CLL) and certain inflammatory disorders. An initial centrifugation at 400×G for 15 minutes was performed. The upper phase was discarded and the lower phase was collected and subjected to Dextran™ sedimentation for 30 minutes in room temperature. After sedimentation, the upper phase containing white blood cells was centrifuged once at 400×G for 10 minutes. The pellet was suspended in Lysis buffer and incubated for 30 minutes in room temperature to get rid of contaminating erythrocytes. Following incubation, density gradient centrifugation, using Lymphoprep™ was performed. The polymorphonuclear (PMN) fraction, containing neutrophils and eosinophils, was collected and subjected to Magnetic Cell Sorting (MACS). Eosinophils were isolated by negative selection using CD16 antibodies conjugated to magnetic microbeads. Purity was confirmed by morphological examination and by staining with May Grunewald-Giemsa solution. Purity was always found to be greater that 95%.
Incubation of CellsIsolated eosinophils (5-10×106/sample) were resuspended in phosphate buffered saline (1 ml/sample) and preincubated for 2 minutes in 37° C. prior to stimulation with ionophore A23187 (1 μM), arachidonic acid (5, 10, 20 or 40 μM) or both for 2, 5 or 10 minutes in 37° C. The reactions were terminated by addition of three volumes of methanol.
Analysis of 15-Lipoxygenase ProductsIn order to get rid of cellular debris and proteins, centrifugation was performed. Supernatants were evaporated under reduced pressure and the residues resolved in methanol and transferred to a test tube. Samples were thereafter evaporated to dryness under a steam of nitrogen, and finally resuspended in 200 μl mobile phase (acetonitril: methanol: H20: acetic acid, 29:19:72:0.8, pH adjusted to 5.6 with NH3). The extracted samples were subjected to analysis in a reverse phase HPLC system, as described. Briefly, samples were applied to an octadecyl reverse phase column (Chromabond C18, Macherey—Nagel, Duren, Germany) and elution rate was 1.2 ml/minute. Eluted compounds were detected and quantified utilising Waters 996 photo diode array spectrophotometer connected to Waters 1996 HPLC system
Mass SpectrometryMass spectrometry was performed as described in Example 1.
Results Biosynthesis of Eoxin C4 in Human EosinophilsWhen analysed by HPLC, one peak with a conjugated triene spectrum (abs. maximum 282 nm) was observed after incubation with arachidonic acid (
Besides expression of 15-lipoxygenase, eosinophils also express 5-lipoxygenase, which generates leukotrienes. Dose-response experiments were carried out in order to optimise the experimental conditions for generation of EoxC4. Also the time course for formation of EoxC4 and LTC4 was investigated (
Taken together the results demonstrate that the eosinophils readily convert exogenous arachidonic acid to EoxC4.
Biosynthesis of Eoxin C4 (14, 15-LTC4) in Human Nasal Polyp TissueA source of airway epithelium is surgical specimens of nasal polyps. Incubation of chopped human nasal polyps with arachidonic acid (40 μM) for 5 minutes led to the formation of 14, 15-LTC4 and a series of 8, 15-DHETE and 14, 15-DHETE metabolites (
The dendritic cells were obtained by separation and cultivation of buffy coat cells (leukocytes) in the presence of growth factors and interleukin-4. The isolated cells showed characteristic function and morphology of dendritic cells. Incubation of these cells with arachidonic acid (40 μM) for 5 minutes led to the formation of mainly 8, 15-DHETE and 14, 15-DHETE but also significant amounts of 14, 15-LTC4 was formed (
In addition to the earlier described 15-LO expression in airway respiratory epithelium, eosinophils, mast cells, and macrophages, the inventors have demonstrated 15-LO expression in several normal and pathological tissues (using antibodies raised against human 15-LO). 15-LO was found to be expressed in lymph nodes from patients with Hodgkin's lymphoma (HL) (
Taken together, the results indicate that 15-LO, and the metabolites formed through this pathway, are involved in the pathophysiology of these diseases.
EXAMPLE 4 Identification of the Enzyme which Converts Eoxin A4 (14, 15-LTA4) to Eoxin C4 (14, 15-LTC4) in L1236 Cells Methods Cell CulturingCell culturing was performed as described in Example 1.
Isolation of Human EosinophilsIsolation of human eosinophils was performed as described in Example 2.
RT-PCR AnalysisIsolation of mRNA from eosinophils and subsequent RT-PCR analysis was performed according to standard procedures. Primers used for the PCR reaction were complementary to microsomal glutathione transferase I (MGSTI), microsomal glutathione transferase II (MGSTII), microsomal glutathione transferase III (MGSTIII) and β-actin (positive control).
Incubation of CellsIsolated eosinophils (5-10×106/sample) were resuspended in phosphate buffered saline (1 ml/sample) and preincubated for 2 minutes in 37° C. prior to stimulation with Eox A4 (10 μM), LTA4 (10 μM) or both for 5 minutes in 37° C. Alternatively, for inhibitor studies, eosinophils were preincubated for 2 minutes in 37° C. in presence of BW70C (1 μM) or MK886 (10 μM) prior to stimulation with ionophore A23187 (1 μM) and arachidonic acid (40 μM) for 5 minutes in 37° C. The reactions were terminated by addition of three volumes of methanol. Metabolites were detected and quantified utilising Waters 996 photodiode array spectrophotometer connected to Waters 1996 HPLC system.
Enzymatic StudiesTo explore the possible involvement of glutathione transferases in the conversion of EoxA4 to EoxC4, recombinant enzymes (1 μg) were incubated with EoxA4 (100 μM) and glutathione (5 mM) for 5 minutes in 37° C. Reactions were terminated by addition of 1 volume of stop solution (AcN: MeOH: HAc, 50:50:1 by volume) and EoxC4 was detected and quantified utilising Waters 996 photo diode array spectrophotometer connected to Waters 1996 HPLC system.
ResultsIsolation, Purification and Characterisation of the Enzyme which Converts EoxA4 to EoxC4 in the Hodgkin Cell Line L1236.
L1236 cells were subcellular fractionated according to standard procedures, and the cytosolic fraction, containing enzymatic activity, was applied to a Glutathione Sepharose column. The bound material was eluted by a glutathione buffer gradient. The eluted fractions were tested for enzymatic activity and run on a SDS-PAGE gel. One single band with an approximate Mw of 28 kD was obtained. Amino acid analysis (PAC), cDNA sequence analysis and BLAST searches revealed that the identity of the obtained band was the soluble glutathione transferase M1b-1b (GSTM1b-1b). Recombinant GSTM1b-1b converted EoxA4 to EoxC4, but did not metabolise LTA4 to LTC4 under identical conditions (
Since GSTM1b-1b is a member of the human soluble glutathione transferase family19, the capacity of soluble glutathione transferases to convert EoxA4 to EoxC4 was investigated. It was demonstrated that, in addition to GSTM1b-1b, also the two isoforms of GSTP1-1 (Val105 and Ile105) had a great capacity to convert EoxA4 to EoxC4 (
To investigate whether the soluble glutathione transferases are involved in EoxC4 formation in eosinophils, a subcellular fractionation of isolated human eosinophils was prepared and incubated with EoxA4. In contrast to L1236, the EoxC4 synthase activity was almost totally located to the membrane fraction in eosinophils (
Since the EoxC4 synthase activity in eosinophils resided in the membrane fraction, the inventors investigated the involvement of membrane associated glutathione transferase in this respect.
Members of the MAPEG (Membrane Associated Proteins in Eicosanoid and Glutathione metabolism) superfamily21 are LTC4 synthase, FLAP (5-lipoxygenase activating protein), PGE synthase, MGSTI (microsomal glutathione transferase I), MGSTII and MGSTIII (3). PCR analysis revealed that eosinophils posses mRNA coding for MGSTII and MGSTIII, whereas no mRNA coding for MGSTI was observed. From earlier studies it was known that eosinophils possess FLAP and LTC4 synthase.
Incubation of the MAPEG family members with EoxA4 and glutathione showed that only LTC4 synthase has the capacity to convert EoxA4 to EoxC4 (data not shown).
LTC4 synthase is traditionally known to be the key enzyme in the biosynthesis of the glutathione containing leukotriene (LT)C4 from LTA4. LTA4 is synthesised via the 5-lipoxygenase pathway. Eosinophils possess both 5-lipoxygenase and 15-lipoxygenase activities, and the result that LTC4 synthase is the only MAPEG family member capable of converting EoxA4 to EoxC4 suggests that LTC4 synthase could have dual activities: LTC4 and EoxC4 synthesis. To test the hypothesis that LTC4 synthase is also the key enzyme in EoxC4 formation, isolated eosinophils where incubated with EoxA4 (10 μM), LTA4 (10 μM), or both for 5 minutes at 37° C. (
Incubation of eosinophils with EoxA4 resulted in biosynthesis of EoxC4, whereas incubation of eosinophils with LTA4 gave rise to LTC4. When the cells were incubated with both substrates, LTC4 and EoxC4 were produced in a 9:1 ratio, approximately. This is in line with previously reported affinities of LTC4 synthase for these substrates20.
To further support the findings that LTC4 synthase also acts as EoxC4 synthase in eosinophils, the inventors performed inhibitory studies.
BW70C is a 5-lipoxygenase inhibitor and MK886 is a FLAP inhibitor, which also block LTC4 synthase when used in higher (10 μM) concentrations (
The assay described herein takes advantage of the ability of lipidhydroperoxides to oxidize diphenyl-1-pyrenylphosphine (DPPP) to a phosphine oxide (see scheme below). Diphenyl-1-pyrenylphosphine is a non-fluorescent compound until oxidized. Oxidation of DPPP yields a fluorescent compound, which is not sensitive to temperature and is stable for at least 60 minutes.
Diphenyl-1-pyrenylphosphine (DPPP) (D-7894) is purchased from Molecular Probes. Cholic acid is purchased from Sigma, linoleic acid from Biomol and PBS from Gibco Life Technologies. Fluorescence is measured using a dual-scanning microplate spectrofluorometer, Spectramax Gemini, from Molecular Devices. The Spectramax Gemini spectrofluorometer uses a Xenon lamp and two holographic diffraction grating monochromators. Microplates with up to 384 wells can be used with the spectrofluorometer. Fluorescent detection is achieved from the top of the well, through the entire depth of the sample in the well.
All reagents are provided in a ready-to-use concentration, except for the fluorophore (DPPP) and the substrate, linoleic acid. DPPP is provided as powder and it should be stored at −20° C. and well protected from light. Linoleic acid is supplied as a 100 mM stock solution in ethanol. Enzyme preparations are provided as frozen aliquots.
The enzyme is expressed using baculovirus and is partially purified from Spodoptera Frugiperdia cells (Sf9) and delivered in Tris-HCl (pH 8.0), 75 mM NaCl and 5% glycerol. The purified enzyme is stable for at least up to 5 months at −70° C. Up to three freeze and thaw cycles do not seem to affect the enzyme activity. However, freeze and thaw cycles of the enzyme should be avoided, if not absolutely necessary. The enzyme is thawed and diluted in PBS just prior to the experiment. Diluted enzyme is to be used within the same day.
DPPP (powder) is dissolved in ethanol and 2-butanol (1:1 ratio) to a final concentration of 0.25 mM. This solution is mixed by vortexing and subsequently sonicated in an ultrasonic waterbath at +4° C. for 10 seconds to completely dissolve DPPP. This solution should be made fresh on the same day as the experiment is performed. The solution should be shaded from light.
Diphenyl-1-Pyrenylphosphine Method for Lipihydroperoxide DetectionThe assay is performed in 96-well all-back plates at room temperature (20-22° C.). each well contains 45 μl consisting of Dulbecco's phosphate buffered saline (PBS) supplemented with 500 μM cholic acid and 15-LO enzyme (pre-mixed). Inhibitor (1 μl) or vehicle (DMSO) is added 5-15 minutes prior to the addition of substrate, 5 μl 1 mM linoleic acid. The plate is then incubated for 20 minutes at room temperature. The enzymatic reaction is terminated by the addition of 50 μl methanol. The plate can now be stored at room temperature for up to 60 minutes without significant loss of lipidhydroperoxides. 50 μl of 25 μM DPPP-solution is added and the plate is incubated at room temperature. After 30-60 minutes, the fluorescence can be read using an excitation wavelength of 355 nm and an emission wavelength of 380 nm.
Due to a low auto-oxidation of DPPP in aqueous solutions, one of the blanks should include buffer, linoleic acid, methanol and DPPP in the same ratios as for the enzymatic reactions.
EXAMPLE 6 Demonstration of the Biological Effects of Eoxin C4, Eoxin D4 and Eoxin E4 (14,15-LTC4, 14-15-LTD4, 14-15-LTE4) EXAMPLE 6a Assessment of Endothelial Cell Barrier Function Materials and Methods Endothelial Cell AssayBovine aorta endothelial cells (BAEC) and human umbilical vein endothelial cells (HUVEC) were isolated and cultured with calf serum or human serum. BAEC or HUVEC in the first to fifth passages were detached by brief (2 min) trypsin-EDTA treatment (0.25% trypsin/0.01% EDTA) and replated onto 3.0 μm pore size polycarbonate filters (Tissue Culture inserts, 10 mm; NUNC, Roskilde, Denmark) or, for the purpose of visual inspection, 0.2 μm pore size Anopore inorganic membrane (transparent when wet). In order to promote cellular differentiation and enhance attachment of EC, the filters were pretreated with 50 μl Biomatrix 1 (167 μg/ml) and air-dried. EC were seeded at a density of 2×105 cells per filter and incubated in culture medium at 37° C. in a humidified atmosphere of 5% CO2 in air. The EC were grown to confluent monolayers, as assessed by daily microscopic observation, in transparent 0.2 μm pore size filters and measurement of the electrical resistance across the monolayer. Under these experimental conditions maximal resistance is obtained at day 7 postseeding, at which day the EC monolayers were then used in the experiments.
Measurement of EC Barrier FunctionRapid changes in endothelial cell (EC) barrier function in response to various arachidonic acid metabolites were analysed through continuous registration of transendothelial electrical resistance (TEER) with electrodes on each side of EC monolayer18. For measurement of TEER, the filter insert with ECs was transferred to a resistance measurement chamber (Endohm-12, World Precision Instruments, Sarasota, Fla., USA) modified so as to assure exact positioning of the electrodes in relation to each other and to the filter insert daring repeated measurements. The chamber (low compartment) and the filter insert (upper compartment) were filled with 2 ml and 400 μl culture medium, respectively. All measurements were made at 37° C. with the equipment placed in a cell culture incubator. Direct readings of the electrical resistance were given by an ohmmeter (Evom, World Precision Instruments, Sarasota, Fla., US) connected to the electrodes of the resistance chamber. The electrical resistance of individual EC monolayers was obtained by subtracting the resistance of the corresponding naked filter coated with Biomatrix as measured prior to seeding of the EC. Thus, TEER values represent the resistance of the EC monolayer solely and depend on the development of tight junctions between adjoining endothelial cells.
Results Biological Effects of 14,15-Cysteinyl-Containing Leukotrienes (Eoxins)Increase of vascular permeability is a marker of inflammation and it is well known that one of the biological effects of cysteinyl-containing leukotrienes is to cause specific plasma leakage in the same way as histamine and bradykinin. In contrast to the 5-lipoxygenase derived cysteinyl-containing leukotrienes, EoxC4 and its metabolites appear not to have contractile effects on guinea pig pulmonary parenchymal strip or ileum. To explore the ability of EoxC4 and its metabolites EoxD4 and EoxE4 to cause plasma leakage, a model system for registration of rapid changes in endothelial cell barrier function was set up. The inventors found that all three 14,15-cysteinyl-containing leukotrienes increased vascular permeability. Concentrations of 10−7 and 10−8 M of the compounds induced significant change in TEER. In comparison, EoxC4, D4 and E4 were about five to ten times less potent than the most potent 5-lipoxygenase derived leukotrienes but more than a hundred times as potent as histamine in this respect (
The oxidative metabolism by the neutrophil and eosinophil can be induced by various agents, e.g. phorbol myristate acetate (PMA), platelet-activating factor (PAF), serum treated zymosan (STZ), immunoglobulins or leukotrienes (LTB4), but also by cytokines, e.g. IL-5 and GM-CSF. Priming refers to a process that leads to an increased responsiveness of the cell to stimulation, without activating the cell. The mechanisms leading to the state of priming of the cells are still unclear, although the hemopoietic cytokines IL-3, IL-5 and GM-CSF have been shown to prime the eosinophil and neutrophil in vitro. However, only IL-5 has been shown to be a selective activator of the human blood eosinophils, while IL-3 and GM-CSF can act on both eosinophils and neutrophils
Materials and MethodsNeutrophil and eosinophil granulocytes were purified from peripheral whole blood using a Percoll gradient and the magnetic cell separation system (MACS).
Granulocytes were primed for 30 minutes at 37° C. with either IL-5 (10.5 ng/mL) or GM-CSF (10.5 ng/mL) and subsequently stimulated with IL-5 (100 ng/mL), GM-CSF (100 ng/mL), LTB4 (10−7M) or Eoxin (10−8-10−6M). Oxidative metabolism was measured by a lucigenin-enhanced chemiluminescence (CL) assay.
The test compound used were EoxC4 (BLX-925), EoxD4 (BLX-926), EoxE4 (BLX-927).
Results Eoxin-Induced Oxidative Metabolism by Non-Primed NeutrophilsThe purified neutrophils were stimulated with two known activators of the oxidative metabolism; the cytokine GM-CSF and LTB4, for comparison with the stimulatory effect of the different Eoxins on neutrophils. Both activators induced the oxygen free radical production by the non-primed neutrophils, while none of the Eoxins induced the oxygen free radical production by non-primed blood neutrophils.
The kinetic curves (
A similar pattern was also seen for EoxC4 (BLX-925). This compound induced the radical production by GM-CSF primed neutrophils in a dose-dependent manner (7-8 subjects of 13 were responders to EoxC4; data not shown).
Eoxin Induced Oxidative Metabolism by Non-Primed EosinophilsAll three Eoxins induced a small production of oxygen free radicals by non-primed eosinophils. However, the produced amount of oxygen free radicals is rather low as compared to other known activators of the oxidative metabolism by eosinophils, in this case the eosinophil specific cytokine IL-5 (
EoxE4 (named BLX-27 in the showed a broad dose-related induction of the radical production by the IL-5 primed eosinophils, illustrated in
EoxC4 (BLX-925) and EoxD4 (BLX-926) induced mainly the oxygen free radical production by GM-CSF primed neutrophils, while EoxE4 (BLX-927) induced mainly the oxygen free radical production by IL-5 primed eosinophils.
EXAMPLE 7 Effect of 15-LO Inhibition on the Formation of Eoxin C4The Hodgkin cell line L1236 was stimulated for 5 min with arachidonic acid (40 μM). L1236 cells efficiently converted arachidonic acid to EoxC4, EoxD4 and a series of 8,15-DHETE and 14,15-DHETE metabolites.
Materials and Methods Cell IncubationThe Hodgkin cell line L1236 (10×106 cells/sample) was suspended in 1 ml PBS-buffer and pre-warmed in 2 minutes at 37° C. prior to addition of test substance (1, 10 or 50 μM). After pre-incubation with the test substance for 5 minutes, arachidonic acid (40 μM) was added. Incubation was stopped after 2 minutes with addition of one volume of methanol. Each test substance concentration was incubated in duplicate.
Solid Phase ExtractionCells and cell debris were removed by centrifugation (2600 rpm, 6 min) from the samples. The supernatant was diluted with water and then transferred to a washed and equilibrated extraction cartridge, Oasis HLB 1 cc 10 mg (Waters, Sweden). The metabolites were eluted with methanol and diluted with water before injected to the HPLC system.
HPLC AnalysisRP-HPLC was performed on a Nova Pak C18 column (2.1×150 mm, Waters AB, Sweden). The initial mobile phase consists of 100% A (0.05% (8.7 mM) acetic acid, with pH adjusted to 5.6 with ammonium) at a flow rate at 0.4 mL/min. A linear gradient was started after five minutes to 36% B (60:40 acetonitrile:methanol) at 20 minutes. The mobile phase was than held isocratic at 64:36, A:B for another 20 minutes. Column effluent was monitored using diode array detection (PDA 996, Waters AB, Sweden) and UV spectra were acquired between 200-340 nm.
Test CompoundsN′-(2-(Ethoxyimino)-1-phenylethylidene)benzohydrazide (Compound F) may be prepared as follows:
(a) Benzoic acid (2-hydroxyimino-1-phenylethylidene)hydrazideBenzoic hydrazide (1 to 1.2 equivalents) was dissolved in an alcoholic solvent (e.g. EtOH or MeOH). Two drops of acid (e.g. concentrated sulfuric acid or glactal acetic acid) were added, followed by the dropwise addition of 2-isonitrosoacetophenone (1 equivalent). The reaction mixture was stirred (e.g. at elevated temperature (e.g. 50-85° C.)), before collecting the solid formed by filtration and, optionally, recrystallising the crude material (e.g. from EtOH/water) to provide the sub-title compound.
(b) N′-(2-(Ethoxyimino)-1-phenylethylidene)benzohydrazideTo a solution of benzoic acid (2-hydroxyimino-1-phenylethylidene)hydrazide (1 equivalent; see step (a) above) and KOH (1 to 1.2 equivalents) in dimethylsulfoxide was added ethyl bromide (at least 1 equivalent). The reaction was stirred at elevated temperature (e.g. 45° C.) for a period of time (e.g. 6 days). Water was added and the mixture was extracted with dichloromethane. The combined organic phase was washed with NaOH (2 M) and water. The organic phase was dried (Na2SO4), evaporated in vacuo and, optionally, recrystallised (e.g. from EtOH/water) to provide the title compound.
3-Chloro-N′-(2-(hydroxyimino)-1-(3-chlorophenyl)ethylidene)benzohydrazide (Compound G) may be prepared as follows:
(a) 2-(3-Chlorophenyl)-2-oxoacetaldehyde oximeIsoamyl nitrite (1.83 g, 15.6 mmol) was dissolved in ice-cold ethanolic sodium ethoxide (0.9 M, 18.3 mL, 16.5 mmol). 3-Chloroacetophenone (14.9 mmol) was added dropwise to the cooled solution, the reaction was allowed to reach room temperature and stirring was continued for 16 h. The solid formed during the course of the reaction was filtered off, washed with diethyl ether, dissolved in water and the aqueous solution acidified with glactal acetic acid. The resultant crystalline solid was filtered off and recrystallised from EtOH/water to provide the sub-title compound.
(b) 3-Chloro-N′-(2-(hydroxyimino)-1-(3-chlorophenyl)ethylidene)benzohydrazide3-Chlorobenzoic hydrazide (1 to 1.2 equivalents) was dissolved in EtOH and to it was added 2 drops of concentrated sulfuric acid and 2-(3-chlorophenyl)-2-oxoacetaldehyde oxime (1 equivalent; see step (a) above). The reaction was heated at 50° C. overnight, filtered, washed with EtOH and recrystallised from EtOH/water to provide the title compound.
Results Inhibition of EoxC4Formation in the Human Cell Line L1236Eicosatetraynoic acid (ETYA) at a concentration of 10−4-4 M, completely blocked the formation of EoxC4, EoxD4 (
L1236 cells were pre-incubated with the indicated substance (1 μM) for two min and subsequently incubated with arachidonic acid (12.5 μM) for five min. Incubation and extraction was performed as described above.
All tested compounds (as described in
CBMC coord blood mast cells
EC endothelial cells
EIA enzyme immuno assay
HETE hydroxyl eicosatetraenoic acid
HPLC high pressure liquid chromatography
IL interleukin
LO lipoxygenase
LT leukotriene
MS mass spectrometry
PG prostaglandin
Human eosinophils contain abundant amounts of 15-lipoxygenase-1 (15-LO-1). The biological role, however, of 15-LO-1 in human is unclear. Incubation of eosinophils with arachidonic acid for five minutes led to formation of a major product with UV absorbance maximum at 282 nm and shorter retention time on RP-HPLC than leukotriene (LT) C4. Analysis with positive ion electrospray tandem mass spectrometry identified the unknown eosinophil metabolite as 14,15-LTC4. This compound could be metabolized to 14,15-LTD4 and 14,15-LTE4 in eosinophils. Also cord blood derived mast cells and surgically removed nasal polyps produced 14,15-LTC4. Incubation of eosinophils with arachidonic acid favoured the production of 14,15-leukotriene C4 over LTC4, whereas challenge with calcium ionophore led to exclusively formation of LTC4. 14,15-cysteinyl-containing leukotrienes induced increased permeability of endothelial cell (EC) monolayer in vitro indicating that these metabolites can induce increased vascular permeability, a hallmark of inflammation. In this model system, 14,15-leukotrienes were almost as potent as LTC4 and LTD4 but 100 times more potent than histamine. Eosinophils produced 14,15-LTC4 after challenge with LTC4, prostaglandin D2 or interleukin-5, demonstrating that 14,15-LTC4 can be synthesized from the endogenous pool of arachidonic acid. Taken together, the present report describes the formation of proinflammatory 14,15-leukotrienes particularly in human eosinophils but also in human mast cells and nasal polyps. Since eosinophils are such an abundant source of these newly characterized metabolites, and to avoid confusion with 5-lipoxygenase derived leukotrienes, we suggest the name Eoxins C4, D4 and E4 instead of 14,15-leukotriene C4, D4 and E4, respectively.
IntroductionThe mammalian lipoxygenases belong to a family of structurally related lipid peroxidizing enzymes that are implicated in the pathogenesis of asthma and other inflammatory disorders. The 5-lipoxygenase (5-LO) is the key enzyme in leukotriene synthesis and this enzyme catalyzes the conversion of arachidonic acid to leukotriene (LT) A4. This compound can be hydrolyzed enzymatically to LTB4 or conjugated with glutathione to form LTC4 which in turn can be metabolized to LTD4 and LTE4. Leukotriene C4 and its metabolites are proinflammatory agents and potent bronchoconstrictors (1). In contrast to 5-LO, much less is known about the biological function of human 15-lipoxygenase (15-LO-1). Human airway epithelial cells, eosinophils and subsets of mast cells and dendritic cells constitutively express high amounts of 15-LO-1 (2-6). A second form of the human 15-LO also exist, which is named 15-LO-2 (7). The amino acid sequence similarity between this enzyme and 15-LO-1 is only 40% (3). Interleukin (IL)4 and/or IL-13 induce the expression of 15-LO-1 in cultivated epithelial cells, monocytes and mast cells (4, 8, 9) and thus these cytokines may act as important physiological/pathophysiological regulators of 15-LO-1 expression in vivo.
15-lipoxygenase-1 has been suggested to be involved in the pathogenesis of bronchial asthma. The amount of 15-LO-1 is significantly increased in the bronchial submucosa of patients with asthma or chronic bronchitis compared to control subjects (10, 11). 15-lipoxygenase-1 converts arachidonic acid to 15-hydroxy-eicosatetraenoic acid (15-HETE), which has been used as a marker for 15-LO activity in vivo as well as in various cells and tissues in vitro. Human tracheal epithelial cells, chopped human bronchi and human lung homogenate convert arachidonic acid mainly to 15-HETE. Lung specimens from asthmatic subjects produced more 15-HETE than specimens from non-asthmatic subjects (12-14) and 15-HETE was the predominant arachidonic acid metabolite in stimulated human lung tissue from atopic and non-atopic asthmatic subjects (15). Increased amounts of 15-HETE were found in bronchoalveolar lavage fluid (BALF) of antigen challenged atopic asthmatic patients (16), in sputum samples from asthmatic subjects (17) and in nasal secretions from healthy control subjects (18). Severe asthmatic patients with persistent airway eosinophilia have higher levels of 15-HETE in BALF compared to healthy subjects, or patients with asthma but without eosinophilia (14). The levels of 15-HETE was found to correlate with sub-basement thickness indicating that 15-LO might be associated with airway remodelling (14).
The most abundant arachidonic acid metabolite generated via the 15-LO pathway is 15(S)-HETE) which is formed from 15(S)-hydroperoxy-eicosatetraenoic acid (15(S)-HPETE). In addition to undergoing reduction to 15-HETE, 15-HPETE may also undergo dehydration to form 14,15-epoxy-eicosatetraenoic acid (14,15-LTA4) (19, 20). Another 15-lipoxygenase product, 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid, has been reported to be a potent chemotactic agent for human eosinophils (21). However, there is also evidence that 15-LO products could have protective roles in inflammatory disorders since 15-LO-1 can be involved in the formation of lipoxins and resolvins (22). Taken together, the physiological and pathophysiological role of the 15-LO pathway in human is not clear.
In this report, we describe the formation and biological effects of 14,15-leukotriene C4, D4 and E4, indicating a proinflammatory role for 15-LO-1 in humans. Since eosinophils are such an abundant source of these newly characterized metabolites, and to avoid confusion with 5-lipoxygenase derived leukotrienes, we suggest the name eoxin C4, D4 and E4 for these novel metabolites instead of 14,15-leukotriene C4, D4 and E4, respectively.
Results Formation of Novel 15-Lipoxygenase Produces in Isolated Human EosinophilsIncubation of isolated human eosinophils with arachidonic acid for five minutes led to the formation of 15 (S)-HETE and 12(S)-HETE in a ratio of approximately 9:1 (data not shown), which is in agreement with the activity of 15-LO-1 (2). A number of peaks with UV absorbance maximum around 270 nm and retention times between 5-7 min were observed in the same chromatogram. In order to get better separation of these more polar metabolites, an acetonitrile based mobile HPLC phase was used. Five peaks containing a conjugated triene spectrum and UV absorbance maximum at 272 nm were identified (
To further analyse the structure of Metabolite 1, samples of human eosinophils incubated with exogenous arachidonic acid were subjected to analyses by LC-MS/MS using a positive ion electrospray tandem mass spectrometry. The obtained ion scan spectrum contained several fragments also present in the spectrum of LTC4 (
In order to analyze if eosinophils can metabolize 14,15-LTC4 to 14,15-LTD4 and 14,15-LTE4, eosinophils were incubated with synthetic 14,15-LTC4 or 14 (R)-cysteinyl-glycyl-15(S)-hydroxy-5,8,10,12(Z,Z,E,E)-eicosatetraenoic acid (14,15-LTD4) for 60 min at 37° C. The metabolites formed were analyzed with product ion scan at 497.2 m/z for 14,15-LTD4 and 440.2 m/z for 14,15-LTE4. The retention time and mass spectrum of a product formed (Metabolite 2) from 14,15-LTC4 were identical to synthetic 14,15-LTD4 (
Human eosinophils contain abundant amounts of both 15-lipoxygenase and 5-lipoxygenase. In order to examine under which conditions the 15-lipoxygenase and 5-lipoxygenase pathways are most active, eosinophils were incubated with either arachidonic acid or calcium ionophore A23187, or both. The cells were incubated for five minutes at 37° C. and the amounts of 14,15-LTC4 and LTC4 were analyzed with RP-HPLC. There is almost no metabolism of 14,15-LTC4 or LTC4 in eosinophils after 5 min of incubation (data not shown). Therefore, measurement of these metabolites is considered to reflect the total formation of 15-lipoxygenase derived cysteinyl-containing 14,15-leukotrienes and 5-lipoxygenase derived cysteinyl-containing leukotriens, respectively. Incubation of eosinophils with exogenous arachidonic acid led to the formation of preferentially 14,15-LTC4 but LTC4 was also formed in some incubations (table 1). Activation of the cells with calcium ionophore A23187 exclusively induced formation of LTC4, while challenge of eosinophils with both ionophore A23187 and arachidonic acid led to the formation of both 14,15-LTC4 and LTC4. Although similar amounts of these metabolites were produced in some incubation, the levels of LTC4 were much higher in certain samples. Taken together, incubations of the cells with arachidonic acid favour the formation of 14,15-LTC4 and calcium activation of the cells triggers the 5-LO and strongly favour the formation of 5-LO derived leukotrienes.
Increase in vascular permeability leading to plasma leakage is a hallmark of inflammation and it is well known that the cysteinyl-containing leukotrienes may contribute to this effect in a similar way as histamine and bradykinin (23). To explore the ability of 14,15-LTC4 and its metabolites 14,15-LTD4 and 14,15-LTE4 to induce alterations in vascular permeability, an established in vitro permeability assay based on assessment of changes in electrical resistance across human endothelial cell (EC) monolayers was used. Maximum stimulus-induced change in EC resistance in this model reaches down to approximately −70%. Dose-response curve show that maximum effect of histamine was obtained at 10−5 M in this model system (data not shown). All 14,15-leukotrienes were capable of inducing maximum increase in EC monolayer permeability (
A possible receptor mediated activation of 14,15-LTC4 formation was investigated by using the allergen induced mast cell mediators LTC4 and prostaglandin (PG) D2 as well as IL-5, which is a potent eosinophil activator. Isolated eosinophils (10×106/sample) were incubated for 5 min, at 37° C. with LTC4 (1 μM), PGD2 (1 μM) or IL-5 (10 ng/ml). Leukotriene C4, PGD2 and IL-5 all induced release of 14,15-LTC4 from eosinophils after 5 min of incubation (table 2). These results demonstrate formation of 14,15-LTC4 from the endogenous pool of arachidonic acid in eosinophils via receptor-mediated mechanisms.
Mast cells play a key role in the pathophysiology of asthma. Recently, we reported that interleukin-4 (IL-4) induced the expression of 15-LO-1 in human cord blood derived mast cells in vitro and that mast cells express 15-LO-1 in vivo (4). Therefore, it was of interest to investigate if mast cells could produce 14,15-leukotrienes. IL-4 primed mast cells were incubated with arachidonic acid (10 μM) for 5 min. Supernatants were collected and analyzed using an EIA against 14,15-LTC4. Under these conditions, human mast cells released 0.8+/−0.6 pmol/106 cells, (n=3), indicating the capacity to synthesise and release immunoreactive 14,15-LTC4 after arachidonic acid stimulation.
The identity of 14,15-LTC4 was further verified with LC-MS/MS single reaction monitoring, SRM. Thus, mast cells incubated with arachidonic acid gave rise to a metabolite with the same retention time and with a typical fragment pattern for the 14,15-LTC4 SRM transition. (data not shown). In addition, mast cell samples were analyzed with a specific 14,15-LTD4 SRM method to investigate whether the 14,15-LTC4 was further metabolised by the cells. Indeed, a metabolite with fragmentation pattern and retention time identical to synthetic 14,15-LTD4 was demonstrated. Taken together, mast cells possess the capacity to produce both 14,15-LTC4 and 14,15-LTD4.
Spontaneous Release of 14,15-LTC4 by Human Nasal PolypsNasal polyposis is a multifactorial disease consisting of tissue infiltration by inflammatory cells such as eosinophils (25). To investigate if 14,15-LTC4 could be synthesized by human nasal polyps, intact surgically removed nasal polyps were washed and incubated in PBS, containing protease inhibitor (Complete MINI®) and indomethacin, at 37° C. for 5 or 30 min. Subsequently, the incubation medium was analyzed using an EIA against 14,15-LTC4. The results demonstrate that nasal polyps spontaneously release 14,15-LTC4 (10.1±0.007 and 7.18±1.18 pmol 14,15-LTC4/g polyp tissue (n=2) after 5 and 30 min incubation, respectively). The decreasing levels of 14,15-LTC4 over time could be due to further metabolism to 14,15-LTD4 and 14,15-LTE4 which is not detected by the antibodies raised against 14,15-LTC4 (cross reactivity less than 1% against 14,15-LTD4 and 14,15-LTE4, see material and methods).
Eoxins—a Suggested Novel Name for 14,15-LeukotrienesThe name leukotriene is traditionally linked to 5-lipoxygenase products. The working name for the 15-lipoxygenase metabolites formed via the 14,15-epoxide in arachidonic acid has been 14,15-leukotriene, although it is not formed via the 5-lipoxygenase pathway. Since eosinophils are a rich source for these novel 15-lipoxygenase products described in this report, and to avoid confusion with 5-LO derived products, we suggest the name eoxin (Eox) C4, EoxD4 and EoxE4 instead of 14,15-LTC4, 14,15-LTD4 and 14,15-LTE4, respectively (
Human airway epithelial cells and eosinophils constitutively express high amounts of 15-LO-1 (3, 5, 6). Also subsets of human mast cells, macrophages and dendritic cells express 15-LO-1 (26+Gulliksson). Despite much work in this research field, the biological role of this enzyme is unclear except the enzyme's function during erythropoeisis (2, 3). In the present report we describe that human eosinophils in particular, but also cord blood derived mast cells and nasal polyps, have the ability to convert arachidonic acid via the 15-LO-1 pathway to metabolites with a conjugated triene spectrum and UV absorbance maximum at 282 nm (
Incubation of eosinophils with exogenous arachidonic acid favoured the formation of 14,15-LTC4 over LTC4 (table 1), while increasing intracellular calcium levels with a calcium ionophore instead triggered 5-LO and led only to the production of LTC4. Thus, the regulation of 5-LO and 15-LO leukotriene production differs and which metabolite that will be the major metabolite excreted will depend on the stimulus. In this respect the 14,15-leukotriene pathway resembles the prostaglandin pathway, occurring readily when free arachidonic acid is available and being independent of calcium fluxes.
In contrast to the 5-lipoxygenase derived cysteinyl-containing leukotrienes, 14,15-LTC4 and its metabolites appear not to have contractile effects on guinea pig pulmonary parenchymal strip or ileum (27). However, we here demonstrate that all three 14,15-leukotrienes increased vascular leakage, a marker of inflammation, in a model system with confluent human endothelial cells. The 14,15-leukotrienes induced increased EC permeability at 10−7 and 10−8 M and were almost as potent as cysteinyl-containing leukotrienes and more than 100 times more potent than histamine in this respect (
Taken together, this report describes the formation of novel proinflammatory arachidonic acid metabolites produced by eosinophils and mast cells, as well as the identification of various physiological triggers for the biosynthesis of these metabolites, Thus, it is possible that activated mast cells and Th2 cells in inflammatory airways excrete LTC4, PGD2 and IL-5, which could induce nearby eosinophils to produce and release eoxins, leading to plasma leakage. Furthermore, in addition to allergic inflammation, it can be speculated that also in non-allergic inflammation, where free arachidonic acid is present in high amounts, eoxin production could occur contributing to the inflammatory process.
Many reports have demonstrated increased amounts and activity of 15-LO-1 in the airway tissues of patients with asthma compared to control subjects. Healthy smokers, but in particular smokers with chronic bronchitis, display an increased expression of 15-LO-1 in bronchial biopsies. In this report we show that the 15-LO-1 pathway can generate the pro-inflammatory 14,15-leukotrienes (eoxins) in eosinophils and mast cells, indicating that inhibition of 15-LO-1 could be an attractive target for treatment of asthma and rhinitis in human.
Material and MethodsVacutainer® blood collection tubes were obtained from Becton Dickinson (Rutherford, N.J.). Paramagnetic microbeads conjugated to monoclonal mouse anti-human CD16 antibodies, magnetic stands and LS+ magnetic separation columns were from Miltenyi Biotec (Bergisch Gladbach, Germany). Recombinant human (rh) IL-4 was bought from In Vitro Sweden AB (Sweden). 14,15-LTC4 EIA kit was purchased from Cayman Chemical (Ann Arbor, Mich.). Ionophore A23187 was purchased from Calbiochem-Boehring (La Jolla, Calif.). Indomethacin was purchased from Sigma-Aldrich. All solvents were of HPLC grade. Arachidonic acid was bought from Nu-Chek prep. Synthetic 14,15-epoxy-5,8,10,12 (Z,Z,E,E)-eicosatraenoic acid (14,15-LTA4), 14(R)-glutathionyl-15 (S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTC4), 14(R)-cysteinyl-glycyl-15(S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTD4), 14(R)-cysteinyl-15(S)-hydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14,15-LTE4), 8(R),15(S)-dihydroxy-5,9,11,13 (Z,E,E,E)-eicosatetraenoic acid (8(R),15(S)-LTB4), 8(S),15(S)-dihydroxy-5,9,11,13 (Z,E,Z,E)-eicosatetraenoic acid (8(S),15(S)-DHETE), 8(S),15(S)-dihydroxy-5,9,11,13 (Z,E,E,E)-eicosatetraenoic acid (8(S),15(S)-LTB4), 8(R),15(S)-dihydroxy-5,9,11,13 (Z,E,Z,E)-eicosatetraenoic acid (8(R), 15(S)-DHETE), 14(R), 15(S)-dihydroxy-5,8,10,12 (Z,Z,E,E)-eicosatetraenoic acid (14(R),15(S)-DHETE or 14(R),15(S)-LTB4), 15(S)-hydroxy-5,8,11,13 (Z,Z,Z,E)-eicosatetraenoic acid (15-HETE), LTC4, LTD4 and LTE4 were from Biomol Inc (Plymouth Meeting, USA).
Isolation of Human EosinophilsVenous blood (100 ml) was drawn from healthy volunteers or from patients with hypereosinophilia, including hypereosinophilic syndrome (HES), chronic lymphocytic leukemia (CLL) and certain inflammatory disorders. An initial centrifugation at 400×g for 15 min was performed. The upper phase was discarded and the lower phase was collected and subjected to Dextran® sedimentation for 30 min at 20° C. After sedimentation, the upper phase containing white blood cells was centrifuged once at 400×g for 10 min. The pellet was suspended in Lysis buffer (100 mM NH4Cl, 10 mM TRIS-HCl, pH 7.4) and incubated for 30 min in room temperature to get rid of contaminating erythrocytes. Following incubation, density gradient centrifugation, using Lymphoprep®, was performed. The polymorphonuclear (PMN) fraction, containing neutrophils and eosinophils, was collected and subjected to Magnetic Cell Sorting (MACS). Eosinophils were isolated by negative selection using CD16 antibodies conjugated to magnetic MicroBeads®. Purity was confirmed by morphological examination and by staining with May Grunewald-Giemsa solution. Purity was always found to be greater than 95%.
Preparation of Cord Blood Derived Mast Cells (CBMCMNC) and Isolation of PolypsCord blood derived mast cells (CBMCMNC) were established as described (4). Polyps were surgically removed and kept in PBS for a maximum of 1 h at 4° C. Polyps were separated from surrounding tissue and washed in PBS w/o Ca2+ and Mg2+. The weight of washed wet polyps was 0.7-1 g.
Cell Incubations EosinophilsIsolated eosinophils (1-20×106/sample) were resuspended in phosphate buffered saline (1 ml/sample) and pre-incubated for 2 minutes in 37° C. (in presence or absence of indomethacin, 1 μM) prior to stimulation with ionophore A23187 (1 μM)/arachidonic acid (1 or 10 μM)/A23187 plus arachidonic acid/PGD2 (1 μM)/LTC4 (1 μM)/IL-5 (10 ng/ml)/14,15-LTC4 (10 μM) or 14,15-LTD4 (10 μM) for indicated time periods at 37° C. The incubations were terminated by addition of one volume of methanol (for analysis by RP-HPLC). For subsequent analysis by enzyme immunoassay (EIA), reactions were terminated by rapid cool off, 0° C., before centrifugation at 1200×g, 5 min. Supernatants were transferred to cryo tubes and stored in −70° C. until analyzed.
Mast CellsPrior to incubation, CBMC cells were primed for four days with IL-4 (10 ng/ml). After mechanical removal and washing in PBS, cells were resuspended in PBS and pre-incubated with or without indomethacin (1 μM) for 2 minutes in 37° C. The CBMC cells were subsequently incubated in 37° C. with arachidonic acid for indicated time periods. Incubations were terminated either by addition of one volume of methanol (LC-MS analysis) or by rapid cool off, 0° C., and subsequently analyzed by EIA.
Human Nasal PolypsHuman washed intact polyps were transferred into clean test tubes containing PBS, protease inhibitor (Complete MINI®) and indomethacin (1 μM) in a total volume of one ml. Samples were incubated at 37° C. for 5 min and 30 min, respectively. Reactions were terminated by rapid cool off, 0° C. and subsequent centrifugation at 1200×g, 5 min. Supernatants were transferred to cryo tubes and stored in −70° C. until analyzed by EIA.
Analysis of 15-lipoxygenase products
Reverse Phase—High Pressure Liquid Chromatography-UV (RP-HPLC-UV)In order to get rid of cellular debris and proteins, centrifugation at 1200×g for 5 min. was performed. Supernatants were evaporated under reduced pressure and the residues resolved in methanol and transferred to a test tube. Samples were thereafter evaporated to dryness under a stream of nitrogen, and finally resuspended in 200 μl mobile phase (acetonitril:methanol:H20:acetic acid, 29:19:72:0.8, pH adjusted to 5.6 with NH3 for analysis of leukotrienes and 14,15-leukotrienes, and methanol:water:trifluoroacetic acid 70:30:0.007 for analysis of monohydroxy acids). The extracted samples were subjected to analysis in a reverse phase HPLC system as described. Briefly, samples were applied to a octadecyl reverse phase column (Chromabond 18C, Macherey-Nagel, Duren, Germany) and elution rate was 1.2 ml/minute. Eluted compounds were detected and quantified utilizing Waters 996 photo diode array spectrophotometer connected to Waters 1996 HPLC system.
Liquid Chromatography-Mass Spectrometry Analysis (LC-MS/MS)After termination of incubations, samples were centrifuged (1400×g, 6 min) and the supernatants were diluted with water to contain maximum 25% methanol and transferred to a washed and equilibrated extraction cartridge, Oasis HLB 1 cc 10 mg (Waters AB, Sweden). The columns were washed with water and eluted with 200 μl methanol to retrieve the metabolites.
Liquid chromatography—mass spectrometry was performed on a Surveyor MS coupled to a TSQ Quantum Ultra triple quadrupole mass spectrometer (Thermo Electron Corporation, Sweden). One volume of water was added to samples prior to injection. Reverse phase LC was performed using a Zorbax Eclipse Plus 3.5 μM C18 column 2.1×50 mm (ChromTech, Sweden) with flow rate constantly held at 400 μl/min. Mobile phase A consisted of 2% acetonitrile in water and 0.1% acetic acid and mobile phase B consisted of 80% acetonitrile in water and 0.1% acetic acid. All water used was of MilliQ grade. Starting isocratically for 1.5 min at 90% A was followed by a 6.5 min linear gradient reaching 100% of B. The system was washed at 100% B for 4 minutes and subsequently equilibrated at 90% A for 4 minutes. The 14,15-leukotrienes were chromatographically separated from leukotrienes by approximately 0.5 min. The mass spectrometer was operated using electrospray atmospheric pressure ionization source in positive mode. The spray voltage was set to 4500 V, capillary temperature was 375° C. and sheath and auxillary gas was optimal at 40 respectively 5 (arbitrary units). Skimmer offset was at 10 V and tube lens 121 V.
LC-MS/MS for Eosinophil MetabolitesLC-MS/MS was utilized to perform product ion scans of protonated 14,15-LTC4, 14,15-LTD4 and 14,15-LTE4. 14,15-LTC4 at 626.2 m/z was fragmented at a collision energy of 22 eV, 14,15-LTD4 at 497.2 and 14,15-LTE4 at 440.2 m/z both at 18 eV.
LC-MS/MS for Mast Cell Metabolites14,15-LTC4 and 14,15-LTD4 was detected by single reaction monitoring, SRM. The transition utilized in the SRM scan was 626 m/z→279 m/z for 14,15-LTC4 and 497 m/z→205 m/z for 14,15-LTD4, both at a collision energy of 20 eV. The transition chosen for 14,15-LTC4 was also present for LTC4, but these two compounds were chromatographically separated by approximately 0.5 minutes. The 497 m/z→205 m/z transition was specific for 14,15-LTD4, and therefore not applicable for LTD4.
Characterization of an Enzyme Immunoassay (EIA) Against 14,15-LTC4An enzyme immunoassay (EIA) against 14,15-LTC4 was developed by Cayman Chemical (Ann Arbor, Mich.) in order to quantify small amounts of 14,15-LTC4. This method was approximately thousand times more sensitive than RP-HPLC in quantifying 14,15-LTC4. The EIA cross reactivities were determined by the manufacturer. The cross reactivity to 14,15-LTD4 and 14,15-LTE4 was 0.9% and 0.04%, respectively. For Leukotriene C4, leukotriene D4, leukotriene E4, arachidonic acid, 12-HETE, 15-HETE, 5(S),6(S)-diHETE, 5(S),15(S)-diHETE, 8(S),15(S)-diHETE and 14,15-diHETE cross reactivity was less than 0.01%.
Supernatants were diluted in EIA buffer and analyses were performed according to the manufacturer's protocol. The optical density (OD) from the EIA determinations was used to calculate % B/B0 according to the relationship:
% B/B0=(sample OD−NSB OD)/(zero standard OD−NSB OD)×100
A standard curve ranging from 7.8-1000 pg/ml (0.012-1.6 pmol/ml) 14,15-LTC4 was generated and used to determine concentrations of 14,15-LTC4 in samples.
Assessment of Endothelial Cell Barrier FunctionHuman umbilical vein endothelial cells (HUVEC) were isolated and cultured as previously described (24). The cells were seeded onto 3 μm pore size polycarbonate filters (Tissue Culture inserts, 10 mm; NUNC, Roskilde, Denmark) at a density of 2×105 cells and grown to confluent monolayers. The capacity of arachdonic acid metabolites to induce changes in barrier function of endothelial cell (EC) monolayers was analyzed through continuous registration of transendothelial electrical resistance (TEER) (24). For measurement of TEER, the filter insert with ECs was transferred to a resistance measurement chamber (Endohm-12, World Precision Instruments, Sarasota, Fla., USA) modified so as to assure exact positioning of the electrodes in relation to each other and to the filter insert during repeated measurements. The chamber (lower compartment) and the filter insert (upper compartment) were filled with 2 ml and 400 μl culture medium, respectively. All measurements were made at 37° C. with the equipment placed in a cell culture incubator. The electrical resistance of individual EC monolayers was obtained by subtracting the resistance of the corresponding naked filter coated with Biomatrix as measured prior to seeding of the EC. Thus, TEER values represent the resistance of the EC monolayer solely.
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Claims
1. A method for identifying a compound for modulating the formation of 14,15-LTC4 (Eoxin C4; EoxC4), 14,15-LTD4 (Eoxin D4; EoxD4), or 14,15-LTE4 (Eoxin E4; EoxE4) in a biological system, the method comprising testing the compound for an effect on 15 lipoxygenase (15-LO) activity or Glutathione S transferase M1-1 (GSTM1-1), Glutathione S transferase P1-1 (GSTP)-1) and/or leukotriene C4 synthase activity.
2. A method for identifying a compound with an inflammation-modulating effect or a bone loss-modulating effect, the method comprising testing the compound for an effect on formation and/or activity of EoxC4, EoxD4 or EoxE4 in a biological system.
3. The method of claim 2 wherein the method is for identifying a compound with an anti-inflammatory effect or a bone loss-reducing effect and the method comprises testing the compound for an inhibitory effect on formation and/or activity of EoxC4, EoxD4 or EoxE4 in a biological system.
4. The method of claim 1 further comprising the step of testing the compound for an effect on formation or activity of EoxC4, EoxD4 or EoxE4 in a biological system.
5. The method of claim 2, wherein the biological system comprises 15-LO, glutathione S transferase (for example GSTM1-1 or GSTP1-1) and/or leukotriene C4 synthase activity.
6. The method of claim 1 wherein the compound is tested in a system comprising a cell fraction or isolated enzyme.
7. The method of claim 1 wherein the compound is tested in a system comprising a cell.
8. The method of claim 7 wherein the compound is tested in a system comprising a cell culture.
9. The method of claim 7 wherein the cell is a L1236 cell or a primary eosinophilic leukocyte or a mast cell.
10. The method of claim 7 wherein the cell is stimulated or incubated with arachidonic acid.
11. The method of claim 7 wherein the compound is tested in a system comprising a tissue or an organ.
12. The method of claim 7 wherein the compound is tested in a system comprising an animal.
13. A method according to claim 7, wherein the compound is tested for an inhibitory effect on Eoxin-induced permeabilisation of endothelial cells in an in vitro model of inflammation; or for an inhibitory effect on Eoxin-induced oxygen free radical production by leukocytes.
14. The method of claim 1 wherein the compound is further tested for an anti-inflammatory effect in an inflammatory disease or in a disease involving inflammatory processes.
15. The method of claim 14 wherein the inflammatory disease or disease involving inflammatory processes is chosen from asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, allergic disorders, rhinitis, inflammatory bowel disease, ulcers, inflammatory pain, fever, atherosclerosis, coronary artery disease, vasculitis, pancreatitis, arthritis, osteoarthritis, rheumatoid arthritis, conjunctivitis, iritis, scleritis, uveitis, wound healing, dermatitis, eczema, psorasis, stroke, diabetes, autoimmune diseases, Alzheimer's disease, multiple sclerosis, sarcoidosis, atherosclerosis, hypertension, Hodgkin's lymphoma and other malignancies.
16. The method of claim 1 wherein the compound is further tested for a bone loss-reducing effect in osteoporosis, osteroarthritis, multiple myeloma, Paget's disease or periodontal disease.
17. A method of making an anti-inflammatory composition comprising
- (i) identifying an anti-inflammatory compound by a method as claimed in claim 2;
- (ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
18. A method of making an Eoxin formation-modulating composition comprising
- (i) identifying an Eoxin formation-modulating compound by a method as claimed in claim 1;
- (ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
19. The method of claim 17 further comprising the step of combining with the composition a further therapeutic agent that is useful in the treatment of inflammation.
20. A method of making a bone-loss-reducing composition comprising
- (i) identifying a bone-loss-reducing compound by a method as claimed in claim 2;
- (ii) combining the compound with a pharmaceutically acceptable excipient or carrier.
21. The method of claim 20 further comprising the step of combining with the composition a further therapeutic agent that is useful in the treatment of bone loss.
22. Use of a L1236 cell or cell culture, or other cell expressing 15-lipoxygenase and at least one of Glutathione S transferase M1-1 (GSTM1-1), Glutathione S transferase P1-1 (GSTP1-1) and leukotriene C4 synthase, in a method for identifying a compound with an inflammation-modulating effect or a bone loss-modulating effect, or for identifying a compound for modulating the formation of EoxC4, EoxD4, or EoxE4 in a biological system.
23. A method for treating a patient in need of promotion of an inflammatory response, the method comprising administering to the patient a therapeutically effective amount of Eox C4, Eox D4 or Eox E4.
24. The use of Eox C4, Eox D4 or Eox E4 in the manufacture of a medicament for treating a patient in need of promotion of an inflammatory response.
25. Eox C4, Eox D4 or Eox E4 for use in medicine.
Type: Application
Filed: Jun 27, 2007
Publication Date: Oct 1, 2009
Inventors: Hans-Erik Claesson (Stockholm), Magnus Bjorkholm (Taby)
Application Number: 12/308,694
International Classification: A61K 31/202 (20060101); C12Q 1/26 (20060101); C12Q 1/48 (20060101); A61P 29/00 (20060101); C07C 57/03 (20060101);
